The present invention relates to aircraft propulsive power units and is particularly concerned with an aircraft propulsive power unit comprising an efflux duct in which gaseous fluid is conducted in a predetermined first flow path for discharge from an exit end of the duct in the production of forward thrust, and a thrust reversing arrangement which in an operative disposition redirects gaseous fluid flowing in the first flow path into a second flow path to produce reverse thrust.
Prior GB 2314818A discloses a thrust reversing arrangement having a flow redirecting structure which includes a redirecting downstream wall against which fluid flow in the first flow path impinges to turn the flow into the second flow path and an upstream wall round which the fluid flow turns and which is so formed as to generate vortices which prevent or delay separation of the boundary layer from the boundary surface.
The propulsive power unit disclosed in GB2314818A is a turbofan power unit which includes a nacelle having a cowl structure to support ambient flow thereover and which in the operative disposition of the redirecting structure occupies a position in which it presents a cowl opening in the cowl structure to allow flow in the second flow path. A cascade assembly extends rearwardly across the cowl opening from a forward end on which it is cantilevered and is so mounted as to extend across the second flow path. It is received within a cavity formed in the redirecting structure when the latter is moved to its inoperative disposition.
When the redirecting structure is moved into its operative disposition in the reversing arrangement disclosed in GB2314818A, the radially outer edge of the downstream wall takes up a position adjacent the rearward end of the cascade assembly to redirect fluid flow directly into and through the cascade assembly.
In the reversing arrangement disclosed in GB2314818A means are provided on the upstream wall to improve the effectiveness of the upstream wall, thus promoting improved flow turning. Although the proposals put forward in regard to the upstream wall can be regarded as an improvement, the relative dispositions of the cascade assembly and the configuration of the downstream wall are not regarded as satisfactory for producing optimum reverse flow conditions.
It is an object of the present invention to provide a flow redirecting structure having one or more features taken individually or in combination which lead to an improved structure and improved reverse flow characteristics.
According to a first aspect of the present invention there is provided an aircraft propulsive power unit comprising an efflux duct in which gaseous fluid is conducted in a predetermined first flow path for discharge from an exit end of the duct in the production of forward thrust, and a thrust reversing arrangement which in an operative disposition redirects gaseous fluid flowing in the first flow path into a second flow path to produce reverse thrust, wherein the reversing arrangement has a flow redirecting structure which is displaceable between an operative disposition and an inoperative disposition and which comprises a flow redirecting zone which intercepts fluid flow in the first flow path and redirects it into the second flow path when the redirecting structure moves to the operative disposition, characterised in that the flow redirecting zone includes a cavity which so forms part of the flow redirecting zone and is so dimensioned as to generate a back pressure which supports redirection of flow.
In an embodiment of the invention according to its first aspect and as hereinafter to be described the flow redirecting zone includes a redirecting wall portion which supports redirection of flow. The redirecting wall portion is so dimensioned and configured as to provide optimisation of back pressure generated by the cavity for predetermined efflux duct flow conditions.
In embodiments of the invention according to its first aspect and as hereinafter to be described the propulsive power unit is a turbofan power unit including a fan duct and the efflux duct is the fan duct of the turbofan unit. The turbofan unit includes a nacelle having a cowl structure to support ambient flow thereover and the flow redirecting structure includes a cowl portion which in the inoperative disposition of the redirecting structure forms part of the cowl structure and supports ambient flow thereover and in the operative disposition of the redirecting structure occupies a position in which it presents a cowl opening in the cowl structure to allow flow in the second flow path.
In an embodiment of the invention according to its first aspect and as hereinafter to be described the thrust reversing arrangement includes a cascade assembly which is so mounted as to extend across the second flow path and which is received within the cavity formed in the flow redirecting zone when the redirecting structure is moved from its operative disposition to its inoperative disposition. The redirecting structure in the inoperative disposition takes up a forward disposition with a leading edge of the cowl portion abutting a trailing edge of an adjacent cowl portion and in the operative disposition takes up a rearward disposition with the leading edge of the cowl portion spaced from the trailing edge of the adjacent cowl portion to provide the cowl opening. The cascade assembly extends rearwardly across the cowl opening from a forward end from which it is cantilevered and terminates at a rearward end at a position in which it is forwardly spaced from the leading edge of the cowl portion when the redirecting structure is in the operative disposition thereby to provide in the second flow path a flow control slot between the rearward end of the cascade assembly and the leading edge of the cowl portion, with the control slot being so dimensioned as to optimise reverse thrust for predetermined fan duct flow conditions.
According to a second aspect of the present invention there is provided an aircraft propulsive power unit comprising an efflux duct in which gaseous fluid is conducted in a predetermined first flow path for discharge from an exit end of the duct in the production of forward thrust, and a thrust reversing arrangement which in an operative disposition redirects gaseous fluid flowing in the first flow path into a second flow path to produce reverse thrust, wherein the reversing arrangement has a flow redirecting structure which is displaceable between an operative disposition and an inoperative disposition and which comprises a flow redirecting zone which intercepts fluid flow in the first flow path and redirects it into the second flow path when the redirecting structure moves to the operative disposition, wherein the propulsive power unit is a turbofan power unit including a fan duct, wherein the efflux duct is the fan duct of the turbofan unit, wherein the turbofan unit includes a nacelle having a cowl structure to support ambient flow thereover, wherein the flow redirecting structure includes a cowl portion which in the inoperative disposition of the redirecting structure forms part of the cowl structure to support ambient flow and in the operative disposition of the redirecting structure occupies a position in which it presents a cowl opening in the cowl structure to allow flow in the second flow path, wherein the redirecting structure in the inoperative disposition takes up a forward disposition with a leading edge of the cowl portion abutting a trailing edge of an adjacent cowl portion and in the operative disposition takes up a rearward disposition with the leading edge of the cowl portion spaced from the trailing edge of the adjacent cowl portion to provide the cowl opening, and wherein a cascade assembly extends rearwardly across the cowl opening from a forward end from which it is cantilevered and the cascade assembly terminates at a rearward end at a position in which it is forwardly spaced from the leading edge of the cowl portion when the redirecting structure is in the operative disposition thereby to provide in the second flow path a flow control slot between the rearward end of the cascade assembly and the leading edge of the cowl portion, with the control slot being so dimensioned as to optimise reverse thrust for predetermined fan duct flow conditions.
In an embodiment of the invention according to its first and second aspects and as hereinafter to be described provision is made for the mounting on the leading edge of the cowl portion a baffle which is so chosen and dimensioned as to optimise the control slot dimension for a predetermined fan duct flow condition. The control slot is furthermore so dimensioned as to optimise back pressure generated by the cavity in the flow redirecting zone.
In an embodiment of the invention according to its first and second aspects and as hereinafter to be described the fan duct includes a fan duct wall which supports fluid flow in the first flow path and the redirecting structure includes a duct wall portion which in the inoperative disposition of the redirecting structure forms part of the fan duct wall and supports flow in the first flow path whilst preventing flow in the second flow path and in the operative disposition of the redirecting structure occupies a position in which it presents a duct opening in the fan duct wall to allow flow in the second flow path. The cascade assembly extends across the second flow path in the region thereof between the duct opening and the cowl opening to control fluid flow in the second flow path. The duct wall portion in the operative disposition of the redirecting structure occupies an obstructing position in which it obstructs flow in the fan duct in the first flow path. The duct wall portion in the obstructing position has its leading edge so positioned as to form a leakage slot providing controlled leakage flow in the first flow path.
According to a third aspect of the present invention there is provided an aircraft propulsive power unit comprising an efflux duct in which gaseous fluid is conducted in a predetermined first flow path for discharge from an exit end of the duct in the production of forward thrust, and a thrust reversing arrangement which in an operative disposition redirects gaseous fluid flowing in the first flow path into a second flow path to produce reverse thrust, wherein the reversing arrangement has a flow redirecting structure which is displaceable between an operative disposition and an inoperative disposition and which comprises a flow redirecting zone which intercepts fluid flow in the first flow path and redirects it into the second flow path when the redirecting structure moves to the operative disposition, wherein the propulsive power unit is a turbofan power unit including a fan duct, wherein the efflux duct is the fan duct of the turbofan unit, wherein the fan duct includes a fan duct wall which supports fluid flow in the first flow path and wherein the redirecting structure includes a duct wall portion which in the inoperative disposition of the redirecting structure forms part of the fan duct wall and supports flow in the first flow path whilst preventing flow in the second flow path, wherein the duct wall portion in the operative disposition of the redirecting structure occupies an obstructing position in which it obstructs flow in the fan duct in the first flow path and wherein the duct wall portion in the obstructing position has its leading edge so positioned as to form a leakage slot providing controlled leakage flow in the first flow path.
In an embodiment of the invention according to its third aspect and as hereinafter to be described, the leading edge of the duct wall portion is so dimensioned and structured as to provide for choking of flow when it passes through the leakage slot and a consequent reduction in leakage flow through the slot.
In an embodiment of the invention according to its third aspect and as hereinafter to be described, the redirecting wall portion extends from the leading edge of the duct wall portion to a forward end of a shelf portion of the redirecting structure. The inner and outer side boundaries of the cavity are formed by the shelf portion and the cowl portion. The cavity extends rearwardly to an end boundary formed by the duct wall portion. The shelf portion extends from the redirecting wall portion rearwardly to the duct wall portion to form with the redirecting wall portion and the duct wall portion a box structure.
In an embodiment of the invention according to its third aspect the redirecting structure includes sealing means to seal off the redirecting wall portion from fluid flow in the fan duct when the redirecting structure is in the inoperative disposition and provision is made to allow fluid under static pressure from the fan duct to flow into the box structure when the redirecting structure is in the inoperative disposition to load the redirecting structure in the direction of the inoperative disposition.
According to a fourth aspect of the present invention there is provided an aircraft propulsive power unit comprising an efflux duct in which gaseous fluid is conducted in a predetermined first flow path for discharge from an exit end of the duct in the production of forward thrust, and a thrust reversing arrangement which in an operative disposition redirects gaseous fluid flowing in the first flow path into a second flow path to produce reverse thrust, wherein the reversing arrangement has a flow redirecting structure which is displaceable between an operative disposition and an inoperative disposition and which comprises a flow redirecting zone which intercepts fluid flow in the first flow path and redirects it into the second flow path when the redirecting structure moves to the operative disposition, wherein the flow redirecting zone includes a redirecting wall portion which supports redirection of flow, wherein the propulsive power unit is a turbofan power unit including a fan duct, wherein the efflux duct is the fan duct of the turbofan unit, wherein the redirecting wall portion forms part of a box structure, wherein the redirecting structure includes sealing means to seal off the redirecting wall portion from fluid flow in the fan duct when the redirecting structure is in the inoperative disposition, and wherein provision is made to allow fluid under static pressure from the fan duct to flow into the box structure when the redirecting structure is in the inoperative disposition to load the redirecting structure in the direction of the inoperative position.
In an embodiment of the invention according to its fourth aspect and as hereinafter to be described, the redirecting structure and the fan duct together form a first displaceable sub-assembly which extends round one half of the turbofan unit and a second displaceable sub-assembly which extends round the other half of the turbofan unit and the box structure comprises a first box portion which extends round the first displaceable sub-assembly and a second box portion which extends round the second displaceable sub-assembly. The first and second box portions are open ended to provide for fluid under static pressure from the fan duct to flow into the box portions to load the redirecting structure in the direction of the inoperative disposition.
In an embodiment of the invention according to its first aspect and as hereinafter to be described, the redirecting structure includes an upstream wall round which fluid flow turns and which is of such convex form as to support adherence of the redirected flow and the redirecting wall portion is so constructed as to conform to the upstream wall when the redirecting structure is in its inoperative disposition.
In an alternative embodiment of the invention according to its first aspect and as hereinafter to be described, the redirecting wall portion of the flow redirecting structure is of planar or substantially planar form and the thrust reversing arrangement includes an upstream wall which extends from the upstream end of the duct opening to an upstream end of the cowl opening and which is so constructed as to conform to the redirecting wall portion.
According to a fifth aspect of the present invention, there is provided an aircraft propulsive power unit comprising an efflux duct in which gaseous fluid is conducted in a predetermined first flow path for discharge from an exit end of the duct in the production of forward thrust, and a thrust reversing arrangement which in an operative disposition redirects gaseous fluid flowing in the first flow path into a second flow path to produce reverse thrust, wherein the reversing arrangement has a flow redirecting structure which is displaceable between an operative disposition and an inoperative disposition and which comprises a flow redirecting zone which intercepts fluid flow in the first flow path and redirects it into the second flow path when the redirecting structure moves to the operative disposition, wherein the flow redirecting zone includes a redirecting wall portion which supports redirection of flow, wherein the propulsive power unit is a turbofan power unit including a fan duct, wherein the efflux duct is the fan duct of the turbofan unit, wherein the fan duct includes a fan duct wall which supports fluid flow in the first flow path and wherein the redirecting structure includes a duct wall portion which in the inoperative disposition of the redirecting structure forms part of the fan duct wall and supports flow in the first flow path whilst preventing flow in the second flow path, wherein the duct wall portion in the operative disposition of the redirecting structure occupies an obstructing position in which it obstructs flow in the fan duct in the first flow path, wherein the redirecting wall portion of the redirecting structure is of planar or substantially planar form and wherein the redirecting structure includes an upstream wall which is so constructed as to conform to the redirecting wall portion.
In an embodiment of the invention according to its fifth aspect and as hereinafter to be described the redirecting wall portion extends from a forward extremity of the duct wall portion radially in the direction of the leading edge of the cowl portion.
According to a sixth aspect of the present invention, there is provided an aircraft turbofan propulsive power unit comprising a core engine, a nacelle housing the engine and having a cowl structure to support ambient flow thereover, a fan duct in which gaseous fluid is conducted in a predetermined first flow path for discharge from an exit end of the duct in the production of forward thrust, and a thrust reversing arrangement which in an operative disposition redirects gaseous fluid flowing in the first flow path into a second flow path to produce reverse thrust, wherein the reversing arrangement has a flow redirecting structure which is displaceable between an operative disposition and an inoperative disposition and which comprises a flow redirecting zone which intercepts fluid flow in the first flow path and redirects it into the second flow path when the redirecting structure moves to the operative disposition, wherein the flow redirecting structure includes a cowl portion which in an inoperative disposition of the redirecting structure forms part of the cowl structure to support ambient flow with a leading edge of the cowl portion abutting a trailing edge of an adjacent cowl portion and in an operative disposition takes up a rearward disposition with the leading edge of the cowl portion spaced from the trailing edge of the adjacent cowl portion to provide a cowl opening, wherein the fan duct includes a fan duct wall which supports fluid flow in the first flow path and the redirecting structure includes a duct wall portion which in the inoperative disposition of the redirecting structure forms part of the fan duct wall and supports flow in the first flow path whilst preventing flow in the second flow path and in the operative disposition of the redirecting structure occupies an obstructing position in which it obstructs flow in the fan duct in the first flow path and in which it presents a duct opening in the fan duct wall to allow flow in the second flow path, and wherein the flow redirecting zone includes a redirecting wall portion which supports redirection of flow characterised in that:
the flow redirecting structure has at least one reverse flow enhancing sub-structure selected from the group consisting of:
(1) a cavity included in the flow redirecting zone which so forms part of the flow redirecting zone and is so dimensioned as to generate a back pressure which supports redirection of flow.
(2) the thrust reversing arrangement includes a cascade assembly which terminates at a rearward end at a position in which it is forwardly spaced from the leading edge of the cowl portion when the redirecting structure is in the operative disposition thereby to provide in the second flow path a flow control slot between the rearward end of the cascade assembly and the leading edge of the cowl portion, the control slot being so dimensioned as to optimise reverse thrust for predetermined fan duct flow conditions.
(3) the duct wall portion in the obstructing position has its leading edge so positioned as to form a leakage slot providing controlled leakage flow in the first flow path.
(4) the redirecting wall portion extends from the leading edge of the duct wall portion to a forward end of a pressure shelf portion of the redirecting structure, the inner and outer side boundaries of the cavity are formed by the pressure shelf portion and the cowl portion, and the shelf portion extends rearwardly to the duct wall portion to form with the redirecting wall portion and the duct wall portion a box structure, the dimensions of which are such as to optimise back pressure in the cavity, and
(5) the redirecting structure includes sealing means to seal off the redirecting wall portion from fluid flow in the fan duct when the redirecting structure is in the inoperative disposition, and provision is made to allow fluid under static pressure from the fan duct to flow into the box structure when the redirecting structure is in the inoperative disposition to load the redirecting structure in the direction of the inoperative position.
Embodiments of the invention according to its different aspects will now be described by way of example with reference to the accompanying drawings in which: